A press of this kind does not have the disadvantages of most conventional presses which are provided with a single revolution clutch for the purpose of ensuring that the press ram carries out only a single cycle of operation each time an electric motor for driving the press ram is actuated. These disadvantages are, mainly, that the press is noisy and jerky in operation and that the single revolution clutch does not reliably ensure that t press ram does not substantially over-run its home position at the end of each cycle of operation. Also, the clutch is unduly subject to wear.
There is described in DE-A-3320023, a press comprising a direct current drive electric motor connected to a slide ram of the press by way of reduction gearing and an eccentric drive shaft, and a control circuit arrangement comprising an incremental encoder for producing a first output representing the angular position of the drive shaft, and thus the linear position of the slide ram and means for controlling the speed of the drive motor to stop the slide ram at least proximate to the home position thereof at the end of each cycle of operation of the slide ram.
The control circuit arrangement of this known press does not serve continuously to monitor the speed of the motor and does not apply a corrective signal to the motor until an overshoot or an undershoot of the press ram has already occurred, so that the ram is not stopped proximate to its home position until several cycles of the press have been carried out.
It is important that the ram should be returned to its home position, that is to say to its fully raised position, with reasonable precision following each cycle of its reciprocating movement, because, for example, the feed finger, of an electrical terminal applicator driven by the press will be incorrectly synchronized with the end positions of the ram of the applicator, should that ram, which is driven by the slide ram of the press, either overshoot or undershoot with respect to its home position at the end of a crimping cycle. Further, any significant overshoot of the slide ram of the press, could cause the ram of the applicator to obstruct the insertion of a lead, to which a terminal is to be crimped during the next ram cycle, between the crimping die and the crimping anvil of the applicator. Proper return of the press slide ram, to its home position at the end of each cycle, is of enhanced importance, where the applicator is part of a lead making machine having automatic lead insertion means which must be synchronized with the cycle of the applicator ram. Further, where the applicator is a stripper crimper, stripping means thereof must also be coordinated with the movement of the applicator ram.